Dependency improvements

[tomwhite]

Lithops has a lot of dependencies in the base package, many of which are not needed when running Lithops.

There are a few things we could do here:

1. Move dependencies for backends into 'extra' packages
   • boto3 - move to lithops[aws] (see #1323)
   • ibm* - move to lithops[ibm]
   • kubernetes?
2. Make dependencies for optional features optional
   • redis
   • pandas/matplotlib/seaborn - for plotting
3. Remove unused dependencies
   • lxml